During drilling operations, especially vertical drilling operations, it is desirable to minimize and control deviations in drilling direction to maintain straight penetration. Conventional bottom hole assemblies for vertical drilling operations utilize concentric stabilizers attached to the exterior of the assembly, and coupled with a bearing assembly, to maintain drilling in a substantially vertical direction. These bottom hole assemblies typically include a single concentric stabilizer secured to the bearing housing of a downhole mud motor, and possibly one or more other stabilizers secured to the drill string above the mud motor. Normally, most bottom hole assemblies utilize one to two stabilizers, having a generally round cross-section, with each stabilizer aligned with one another in a generally parallel configuration.
Despite use of stabilizers and standard mud motors, conventional bottom hole assemblies remain subject to directional deviations, especially when penetrating through medium to hard formations, due to insufficient stability and stiffness in the lower portion of the drill string and assembly.
Further, the shape and arrangement of the stabilizers in typical assemblies has failed to maximize the lifespan of assembly components while maintaining bore size and integrity. Use of conventional stabilizers has achieved a less-than-optimal flow area around the stabilizers, resulting in a greater-than-optimal annular velocity. The increased annular velocity can wash out the wellbore, resulting in a reduction in the effectiveness of the assembly when drilling a vertical hole.
Additionally, conventional downhole mud motors experience a large degree of undesirable flexibility and wear, due to multiple internal connections within the motor, which can contribute to deviations in drilling operations while reducing the life expectancy of the motor and other assembly components.
A need exists for a vertical drilling system that uses stabilizers having a triangular cross section, that are rotationally offset from adjacent stabilizers to provide an improved measure of stiffness, an improved flow area, and a reduced annular velocity.
A further need exists for a vertical drilling system that provides improved resistance to bending and improved directional control to a drill string through use of at least three stabilizers secured between a mud motor stator housing and the drill bit, which provides the dual benefit of an increased penetration rate due to an increased amount of weight placed on the drill bit.
A need also exists for a vertical drilling system having a one-piece motor transmission housing and internal drive shaft that utilizes only two connections to communicate with the drill bit, providing improved reliability while enabling the system to undertake high torque operations.
The present embodiments meet these needs.